Testing for heavy metals: blood, urine or hair, which test is worth it

An evaluation of 21 environmental and occupational studies that measured lead in both blood and bone showed: in environmentally driven exposure, bone lead, that is the cumulative dose, was more strongly and more consistently linked to cognitive findings than blood lead. For you this means: a normal blood lead value does not rule out a legacy burden built up in the bone over years.

A methodological overview of cadmium measurements sums up: cadmium in blood reflects rather the most recent exposure, cadmium in urine mirrors the body burden and the cumulative long-term exposure. For a chronic cadmium question the urine is therefore the more fitting matrix than the blood.

In a review of mercury poisoning from skin-lightening cosmetic products, the author sums up the measurement logic like this: the blood level drops again within days after a short exposure, so blood is mainly suited to fresh, higher exposures. Urinary mercury is regarded as the best marker of the body burden, preferably as a 24-hour collection, alternatively as spot urine referenced to creatinine. The same source describes a chelating agent as an antidote in a confirmed poisoning, not as a screening test for unclear symptoms.

In a study of workers and control persons, an elevated total and arsenobetaine arsenic was tied to the consumption of crustaceans and shellfish in the last three days. Only the speciation separated the diet from a real exposure. For you this means: without fish avoidance and separate measurement of the inorganic species, a fish meal can create a false finding.

In 210 Japanese men without occupational exposure, arsenobetaine and dimethylarsinic acid (DMA) made up the largest part of the urinary arsenic, which is likely to be due at least in part to the high fish consumption. The authors therefore recommend subtracting DMA when assessing the inorganic burden. One addition that often gets lost: arsenobetaine is regarded as largely harmless, DMA is not in the same way. DMA is also formed in the body from inorganic arsenic and is therefore not a pure fish marker. So it is not enough to strip everything organic out of the total value. It takes a clean breakdown of the individual species and a medical interpretation.

In Cornwall, drinking water and urinary arsenic including speciation were measured in 207 people. The unadjusted total urinary arsenic correlated only weakly with the water exposure, because arsenobetaine from seafood overlaid the picture. Only the sum of the inorganic species correlated strongly. A total value without speciation can therefore completely obscure the actual source.

In 400 four-year-old children, inorganic arsenic and MMA rose with rice products, arsenobetaine with seafood. Both sources could be clearly told apart via the speciation. For you this means: whether the arsenic comes from rice (toxicologically relevant) or from fish (largely harmless) can only be clarified by speciation.

A pharmacokinetic model calibrated on human data shows: the biological half-life of methylmercury varies individually from under 30 to over 120 days, governed among other things by gut biotransformation and muscle mass. This is a computational model, not a value measured directly in an individual person. It means a single blood value remains a snapshot, and it makes timing and abstinence before the test important.

In a biomonitoring pilot study, mercury, lead and cadmium were measured in the morning urine of 170 adults, and the geometric means were reported referenced to creatinine. It is exactly this reference that makes urine values comparable in the first place, without it a value can look low simply because of heavy drinking.

Researchers split a single hair sample from a healthy person and sent it to six commercial US laboratories, which together covered around 90 percent of the market. The results for the same sample differed by more than tenfold for 12 minerals, with contradictory classifications and recommendations. For you this means: a hair self-test can deliver a different result depending on the laboratory, as a stand-alone burden marker it is unreliable.

The German Human Biomonitoring Commission derives reference values for arsenic, cadmium, lead and mercury from large population surveys, each separately for blood or urine. One thing matters here: both works cited on this page refer to children. Adults have their own values, for example from the German Environmental Survey. For you this means being doubly careful. Whether a value is elevated depends not only on the matrix, but also on whether the reference value applies to your age group at all. A children's value applied to an adult finding can mislead in both directions.

Based on a representative children's survey, the reference values were updated and partly lowered, still separated by blood and urine. This means: reference values are matrix-bound and change over the years. An old finding is not necessarily still normal by today's standard.

In a national biomonitoring, blood, spot urine, hair and breast milk were examined in 1084 people. Seafood raised mercury and arsenobetaine, smoking and game meat the cadmium, amalgam the mercury, regional legacy sites shaped lead and mercury, differently depending on the matrix. A multi-matrix picture is therefore more informative than a single value.

In a cross-sectional comparison, long-term exposed residents were compared with control persons. The urinary cadmium rose with age and with the extent of exposure and correlated with tubular markers such as beta-2-microglobulin, as an expression of the body burden. This suggests that urinary cadmium can reflect a burden built up over years that a single blood value misses. A cross-section can compare a snapshot, not a course over time.

A review from 1995, written by the working group that substantially co-developed the DMPS test, described urinary mercury after chelation as a possibly more sensitive marker of low exposure than unprovoked urine. The authors called the principle promising at the time. Thirty years later, that hope has not carried the field. I name the source here because it explains the thinking behind the test, not because it proves it.